1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member having an interlayer which contains a resin of a specified structure.
The present invention also relates to a process cartridge and an electrophotographic apparatus employing the above electrophotographic photosensitive member.
2. Related Background Art
The electrophotographic photosensitive member has normally a photosensitive layer on an electroconductive support. Usually the photosensitive layer is extremely thin, and its thickness is liable to be irregular at defect points on the surface of the support: such as scratches and adhering matter. This liability to irregularities is particularly significant in the widely used function-separation type photosensitive layer constituted of a charge-generating layer as thin as 0.5 .mu.m and a charge-transporting layer.
The photosensitive layer is required to be formed as uniformly as possible in thickness since an irregularity in thickness thereof will give rise to irregularity of potential or sensitivity.
Another important characteristic property of the electrophotographic photosensitive member is stability of light area potential and dark area potential during repeated use. Without the potential stability, the formed image density will be unstable or the formed image will be fogged.
To offset such disadvantages, an interlayer is provided which serves to cover any surface defects of the support, to improve adhesion of the support with the photosensitive layer, and to prevent carrier injection from the support into the photosensitive layer.
The interlayer is conventionally formed from a resin: including polyamide resins (Japanese Patent Application Laid-Open Nos. 48-47344 and 52-25638), polyester resins (Japanese Patent Application Laid-Open Nos. 52-20836 and 54-26738), polyurethane resins (Japanese Patent Application Laid-Open Nos. 53-89435 and 2-115858), quaternary ammonium salt-containing acrylic polymers (Japanese Patent Application Laid-Open No. 51-126149) and casein (Japanese Patent Application Laid-Open No. 55-103556).
The interlayer formed from any of the above materials, however, changes its electric resistance depending on temperature and humidity. Therefore, an excellent electrophotographic photosensitive member is not obtainable which has excellent and stable potential characteristics throughout all the environmental conditions from low-temperature and low-humidity to high-temperature and high-humidity.
For example, when the photosensitive member is repeatedly used under the conditions of low temperature and low humidity where the electric resistance of the interlayer tends to rise, the electric charge tends to remain in the interlayer, resulting in rise of light area potential and residual potential. Consequently, the copied image becomes fogged during normal development or the image becomes thin during reversal development, being incapable of giving continuously a desired quality of recorded images.
On the other hand, under the conditions of high temperature and high humidity, the barrier function of the interlayer tends to decline to increase carrier injection from the support, whereby the dark area potential falls. Consequently, the copied image becomes thin in normal development, or the image exhibits black dot-shaped defects or becomes fogged in reversal development.
Moreover, the interlayer frequently causes decrease in the sensitivity of the photosensitive member, even if the interlayer improves the stability of potential at low temperature and low humidity, and prevents formation of black dot-shaped defects in the image at high temperature and high humidity.